For this example, we will encode the title of this post.

The first is “ROT-13 encoding,” which despite it’s name isn’t really an encoding. ROT-13 substitutes each letter with the letter 13 away (half an alphabet), which eliminates the need to define a direction in the shift. A becomes M, M becomes A. D becomes P, P becomes D.

S transliterates to F, i<=>v, m<=>z,p<=>c, l<=>y,e<=>r. Thus Simple becomes Fvzcyr

Simple Ciphers Demonstrated
Fvzcyr Pvcuref Qrzbafgengrq

ROT 13 is convenient in that the cipher wheel can really be written with only half the wheel, since all mappings are bi-directional. S becomes an F and an F becomes an S. This also makes deciphering the message simple since, technically, you can simply re-cipher the text and it will revert to the original plaintext

Second is a “Rotation Cipher,” more commonly known as a “Caesar Cipher,” which is actually a more general version of ROT-13. A Rotation Cipher would generally be named with a direction and a number. ROT Right 5, or ROT-L-9. ROT-13 is a special case because L and R would be identical (26 letters, 13 is halfway around, either direction). Rotation Ciphers are frequently put on “secret decoder rings.”

In this instance we have S mapping to N, I to D, M to H, P to K, L to G, and E to Z. Simple becomes NDHKGZ

Simple Ciphers Demonstratred
Ndhkgz Xdkczmn Ynhjinomvomny

Rotate Right 5 is somewhat more complicated than ROT13, simply because the mappings are not bi-directional. However, given the S to N mapping, it is possible to deduce the full cipher. In fact, that is how I ciphered the “Ciphers Demonstrated” portion. C is two letters before E. E was Z, thus C is X. I was in Simple, as was P. H is immeditely before I, e occurs in both, R is one less than S, S appears in both. Thus only three letters needed to be “deduced” for enciphering “Ciphers”, and none was more than two letters off of a letter we had already. The same holds true for “Demonstrated”

The third is the generic case of “substitution cipher.” In this instance, A may be mapped to X and then B to C, there is no relation between mappings. This can either be a 13-letter table (where, then, X would map to A and C to B) or a full 26 (C may map to A, and X would become I).

S maps to E. I maps to M, M maps to Z and NOT I. P maps to Y. L to K, and E to G. Simple maps to Emzykg.

Simple Ciphers Demonstrated
Emzykg Amyugse Ogzhrevsxvgo

I made a note that M mapped to Z and not I. The process of enciphering this text could be made “easier” by making any given cipher pair a bidirectional pairing. I to M and M to I. But that also simplifies the algorithm and makes it simpler for an “attacker” to “crack” the “code”. (I put those words in quotes because, honestly, there’s not much code to crack in this instance)

The first is “ROT-13 encoding,” which despite it’s name isn’t really an encoding. ROT-13 substitutes each letter with the letter 13 away (half an alphabet), which eliminates the need to define a direction in the shift. A becomes M, M becomes A. D becomes P, P becomes D.

Second is a “Rotation Cipher,” more commonly known as a “Caesar Cipher,” which is actually a more general version of ROT-13. A Rotation Cipher would generally be named with a direction and a number. ROT Right 5, or ROT-L-9. ROT-13 is a special case because L and R would be identical (26 letters, 13 is halfway around, either direction). Rotation Ciphers are frequently put on “secret decoder rings.”

The third is the generic case of “substitution cipher.” In this instance, A may be mapped to X and then B to C, there is no relation between mappings. This can either be a 13-letter table (where, then, X would map to A and C to B) or a full 26 (C may map to A, and X would become I).

In terms of data security, none of these is any good. These are more useful for either pre-coding a message for actual encoding or encryption, or for passing insecure data. There are ways to complicate these techniques (which I will work up separately), which make them more secure.

The basic use for a Simple Cipher is to make data require some level of work to read (to slow someone down), and to make for ready manual processing. With the “decoder ring”, anyone can easily tick through an arbitrarily long message with a consistent time per letter, and a consistent process.

(This is a post I’m migrating from the first edition of this blog)